(1) Field of the Invention
The present invention relates to circuits for modeling diodes and varistors required in circuits such as signal limiting circuits used in telephone transmission equipment.
(2) Description of the Prior Art
Previously, diode or varistor devices were multipled in either a series or parallel configuration so as to vary the effective forward breakdown or threshold voltage. But, no similar technique was available for materially changing the active region characteristics of these devices. Alternately, new devices would be developed for particular applications. However, this was an iterative process requiring well defined voltage-current relationships which would not always be available. In a common implementation of an "ideal diode" an operational amplifier is utilized as a threshold detector with its output tied across the circuit reference element. A technique similar to this was disclosed by Eugene R. Schlesinger in an article appearing in Electronic Design on Apr. 26, 1977. As with other techniques, this one also did not provide for control in the active region of the diode characteristic.